I know that many have given up and returned this device (JBL Link Bar), but I'm still soldiering on, some others may be too.
About two weeks ago I noticed that a bunch of really basic "Hey Google" commands stopped working, for example "Hey Google, volume 30%". If the TV was off then I'd get some form of "Sorry I don't know how to do that yet", if the TV was on then I'd get a bunch of YouTube search results related to volume increase (e.g. increase hair volume!!!).
This clearly wasn't related to any action that I'd taken and was due to something either on the backend or an application updated.
I contacted JBL yesterday and (unfortunately), just got asked to reset the device - twice!
What I did notice when I did the reset was that immediately after the reset, before any updates, the volume command returned to normal. This confirmed that one of the updates introduces the problem.
I decided to review the apps that are updated and figured that the "Google app for Android TV" looked like it was most likely to be associated with the symptom. I've "Uninstalled" the app, which actually reverts it back to the original reset version AND disabled automatic updates.
This workaround restores the volume control via "Hey Google" and I've not noticed any negative side affects at this point.
I'll intermittently try updating the app and uninstalling it to see if the app has been fixed. My guess is that either Google have a bug in the app, or JBL should and didn't test it before allowing it's release to their devices.
Hope this is useful!
I bought a heavily discounted "factory refurb" JBL smart speaker. I'm guessing they have an unusual high rate of return because of their buggy software than defective parts.